Apollo 9 was the third manned mission in the United States Apollo space program and the first flight of the Command/Service Module (CSM) with the Lunar Module (LM). Its three-person crew, consisting of Commander James McDivitt, Command Module Pilot David Scott, and Lunar Module Pilot Rusty Schweickart, tested several aspects critical to landing on the Moon, including the LM engines, backpack life support systems, navigation systems, and docking maneuvers.